The proposed research is in developing an automatic digital imaging system for Megavoltage Radiotherapy Machines. This system will have good contrast resolution to delineate boney landmarks in the image of a radiation treatment portal. Objectives are: (1) Replace port filming procedure for treatment portal verification, (2) Correct erroneous portal during treatment and, (3) Enable therapy machine to function as a simulator. Two types of imaging devices will be studied: (1) A scanning linear array (or multiple linear arrays) of detectors which sweeps across the radiation transmitted through the patient, (2) Fluorescence screen and low light level television camera. A mini-computer is required to manage the imaging system and analyze the protal errors. In order to verify the accuracy of treatment portal efficiently, the correct position of boney landmarks obtained from the simulation film is digitized and super-imposed on the portal image obtained by the imaging device. Patient records are stored more compactly than film on magnetic tape or disk. On-line portal correction can be effected by installing remote control in the motion of the therapy machine. The therapy machine with imaging and remote control capabilities can function as a simulator as well. This facilitates patient simulation for small radiation therapy clinics which do not possess a simulator. In addition, the merits of the system in terms of quality control and cost saving to patients will be evaluated. Since the daily treatment portal are recorded, it has a tighter quality control in the portal accuracy. The reduction in Localization Error can be compared with those which use the conventional port film method. Cost saving can be estimated from the time taken by the port filming procedure since the automatic imaging system takes negligible time.